The neutron and its role in cosmology and particle physics

Experiments with cold and ultracold neutrons have reached a level of precision such that problems far beyond the scale of the present Standard Model of particle physics become accessible to experimental investigation. Due to the close links between particle physics and cosmology, these studies also permit a deep look into the very first instances of our universe. First addressed in this article, both in theory and experiment, is the problem of baryogenesis ... The question how baryogenesis could have happened is open to experimental tests, and it turns out that this problem can be curbed by the very stringent limits on an electric dipole moment of the neutron, a quantity that also has deep implications for particle physics. Then we discuss the recent spectacular observation of neutron quantization in the earth's gravitational field and of resonance transitions between such gravitational energy states. These measurements, together with new evaluations of neutron scattering data, set new constraints on deviations from Newton's gravitational law at the picometer scale. Such deviations are predicted in modern theories with extra-dimensions that propose unification of the Planck scale with the scale of the Standard Model ... Another main topic is the weak-interaction parameters in various fields of physics and astrophysics that must all be derived from measured neutron decay data. Up to now, about 10 different neutron decay observables have been measured, much more than needed in the electroweak Standard Model. This allows various precise tests for new physics beyond the Standard Model, competing with or surpassing similar tests at high-energy. The review ends with a discussion of neutron and nuclear data required in the synthesis of the elements during the "first three minutes" and later on in stellar nucleosynthesis.Comment: 91 pages, 30 figures, accepted by Reviews of Modern Physic

Evolution of γ\gamma Collectivity — (n,γ)(n,\gamma ) Spectroscopy of 98^{98}Mo with FIPPS

International audienceExcited states in 98Mo have been populated in (n,γ) reaction and studied using γ-ray coincidences measured with Germanium Clover detectors of the new instrument FIPPS. The aim of the study is to investigate the evolution of γ collectivity in Mo isotopes in its early-development stage. The ground state of 97Mo 5/2+ should allow the observation of the γ band in 98Mo up to spin 7+. This is sufficient to measure interesting properties of the γ band, such as mixing ratios

Study of parity-doublet structure in the 147^{147}La nucleus

International audienceThe work reports several new excited states in the neutron-rich 147La nucleus, populated in spontaneous fission of 252Cf. The excitation scheme has been reinvestigated by means of γ-ray spectroscopy, using high-fold γ coincidences measured with the Gammasphere array of Ge detectors. It is shown that the 229.65-keV level has spin and parity 11/2-, which changes the 9/2- spin-parity reported in a recent evaluation and sets up the spinparity of the ground state as 5/2+. New levels allow to arrange the excitation scheme of 147La into a parity-doublet-like structure showing that the 147La nucleus may have an octupole deformation

Low-spin excitations in <math><mmultiscripts><mi>Zr</mi><mprescripts/><none/><mn>95</mn></mmultiscripts></math>

International audienceThe low-spin structure of the Zr95 nucleus was investigated at Institut Laue-Langevin (Grenoble) by employing three complementary methods: Either cold-neutron capture on Zr94 or cold-neutron-induced fission of U235, both using the highly efficient EXILL array of high-purity germanium (HPGe) detectors, or β decay of mass-separated Y95 ions at the focal point of the Lohengrin fission-fragment separator. Together 21 new levels and 44 new transitions were placed in the level scheme. Spin-parity assignments to most of the levels in Zr95 were significantly improved

Parity-doublet structure in the _{57}^{147}La_{90} nucleus

International audienceExcited states in La147, populated in spontaneous fission of Cf252, have been reinvestigated by means of γ-ray spectroscopy, using high-fold γ-ray coincidences measured with the Gammasphere array of Ge detectors. The 229.5-keV level, which has been assigned spin parity 9/2− in a recent evaluation, is shown to have spin parity 11/2−. Consequently, the ground state has spin parity 5/2+. Excited levels in La147 have been arranged into a parity-doublet structure, showing that at medium excitation energy the La147 nucleus may have octupole deformation. The B(E1) rates in La147, which are factor of four lower than in La145, suggest that the electric dipole moment in La147 is depressed by an extra mechanism, probably connected with the population of particular neutron orbitals